This invention relates to polymerizable compositions and in-mold cured products obtained from such compositions (hereinafter referred to simply as "molded products").
Polymerizable compositions containing polymerizable liquid resins are widely in use. For example, molded products of polymerizable compositions containing unsaturated polyester resin, which is a representative example of polymerizable liquid resin, are being used as external panels and accessaries of automobiles. There are a number of molding methods available for obtaining molded products of polymerizable compositions, including the compression molding which uses sheet molding compound (SMC), the injection molding which uses bulk molding compound (BMC), the hand lay-up method whereby polymerizable compositions impregnate a reinforcing fiber mat, textile or strands and are hardened, the pultrusion method, and the resin transfer molding (RTM) and reaction injection molding (RIM) methods whereby a polymerizable composition is introduced into a mold for quick in-mold curing.
As examples of prior art polymerizable compositions containing unsaturated urethane, Japanese Patent Publication Tokkai 57-182312 and Japanese Patent Publication Tokkai 61-225210 have disclosed compositions containing polymerizable liquid resins comprising unsaturated urethane and alkyl (meth)acrylate obtained from polyisocyanate and hydroxyl alkyl (meth)acrylate.
The aforementioned prior art polymerizable compositions, however, have the following disadvantages because of their use of unsaturated urethane obtained from polyisocyanate and hydroxy alkyl (meth)acrylate:
(1) Since unsaturated urethane thus obtained contains many urethane bonds within its molecule, it is inferior in water resistance, like most other kinds of polyurethane liquid resin, as compared to other thermosetting polymerizable compositions. This limits the use of the molded products obtained by in-mold curing; and
(2) Since the density of cross-links is high in such molded products obtained by in-mold curing, shrinkage in hardening is large compared to unsaturated polyester liquid resins. As a result, generation of cracks and appearance of fiber patterns are prominently observed. Low shrinkage agents may be used for preventing such phenomena but they are not very effective.